Related for Demai 4:1
הַלּוֹקֵחַ פֵּרוֹת מִמִּי שֶׁאֵינוֹ נֶאֱמָן עַל הַמַּעַשְׂרוֹת, וְשָׁכַח לְעַשְּׂרָן, וְשׁוֹאֲלוֹ בְשַׁבָּת, יֹאכַל עַל פִּיו. חָשְׁכָה מוֹצָאֵי שַׁבָּת, לֹא יֹאכַל עַד שֶׁיְּעַשֵּׂר. לֹא מְצָאוֹ, אָמַר לוֹ אֶחָד שֶׁאֵינוֹ נֶאֱמָן עַל הַמַּעַשְׂרוֹת, מְעֻשָּׂרִין הֵן, אוֹכֵל עַל פִּיו. חָשְׁכָה מוֹצָאֵי שַׁבָּת, לֹא יֹאכַל עַד שֶׁיְּעַשֵּׂר. תְּרוּמַת מַעֲשֵׂר שֶׁל דְּמַאי שֶׁחָזְרָה לִמְקוֹמָהּ, רַבִּי שִׁמְעוֹן שְׁזוּרִי אוֹמֵר, אַף בְּחֹל שׁוֹאֲלוֹ וְאוֹכְלוֹ עַל פִּיו:
One who buys produce from one who is not trustworthy concerning tithing and forgot to tithe it; and asks him [the vendor] on Shabbat, may eat it by his [the vendor's] word. At nightfall at the conclusion of Shabbat, he may not eat until he has tithed [the produce]. If he did not find him [the vendor on Shabbat], [and] another individual who is not trustworthy concerning tithing says to him, "They are tithed," he can eat by his word. At nightfall at the conclusion of Sabbath, he may not eat until he has tithed. [In terms of the] <i>Terumat Ma'aser</i> [a portion of the tithes that is given to the priest] of <i>Demai</i> [produce from which it is uncertain if tithes were already taken] that returned to its place [was mixed back into the produce from which it was taken], Rabbi Shimon Shezuri says, "Even on a weekday, he asks him and eats by his [the vendor's] word."